1. Field of the Invention (Technical Field)
The presently claimed invention relates to automated testing and more particularly to methods and apparatuses for the production testing of passive electronic interconnects to evaluate the frequency dependent loss characteristics.
2. Background Art
Interconnects including cables, cable assemblies, connectors, and printed wiring board traces that support fast data transfer rates can experience higher and varied attenuation profiles depending on the non-repeatability in their manufacturing processes. There is a shortage of test methodologies and equipment to measure signal loss in a production environment for passive interconnects such as cables, connectors, and printed wiring board traces. The bulk of the current art for measuring loss, including vector network analyzers, utilizes swept frequency test signals through the device under test to determine changes in amplitude and phase. These methods are typically utilized in a laboratory environment and require a specific skill set to calibrate, operate and to interpret the measurement results. The cost of the equipment is usually high and many times prohibitive due to the cost and complexity.
Other current prior art systems involve the use of Time Domain Transmission (TDT) instrumentation to capture data that is then coupled with mathematical techniques, such as Fourier transforms, to convert the collected data into a format that can be displayed in the frequency domain similar to the data from vector network analyzers. This method does reduce the operational sophistication of the measurement process and can reduce the cost of the process. However, these techniques have been limited to processes involving the use of test structures that are different from the actual product to be tested. Short Pulse Propagation and Single Ended Transmission to Differential Insertion Loss (SET2DIL) are two techniques that utilize test coupons in this fashion to assess the loss for printed wiring board traces. A test coupon is defined as a device that is utilized for testing and that is manufactured alongside a PC board that can later be broken away for specific tests. A limitation in these methods is that the test structures within these test coupons are designed to represent the actual interconnect, but often can have different network characteristics than the actual printed wiring board traces.
Other related systems involve the testing of cables utilizing time domain methods and equipment. These methods include injecting signals from one end of the cable and measuring responses from the other end of the cable, injecting signals from one end of the cable and measuring the response from the same end of the cable with termination impedance at the far end, which substantially matches the impedance of the cable, and injecting signals from one end of the cable and measuring the response from the same end of the cable with an open termination at the opposite end.
These systems have limitations in the calibration methodology and the processing of the response waveforms to achieve the measurements. The focus of these related systems is to resolve discontinuities that may exist in cable assemblies due to splices, branching of the cable or other defects and not on passive interconnects.